My first post so be gentle with me.
I have recently upgraded my Nikon D40 to a Nikon D3100 and I'm very happy with it. I also have the standard 18-55 lens and a Nikon 80-300 zoom which I use for Car rallying and other motor sport use. I also have a Sigma 150-500 which I tend to use for wildlife.
Recently I've been experimenting with moon photgraphs and have hit a snag.
Using the 80-300 on max. zoom I can set the lens to manual focus and the camera to 'S' priority to play with different shutter speeds. Even though the camera says 'image too dark' it will still take reasonable pictures by changing shutter speeds.
However, when I switch to the Sigma, even though I can overide to manual focus, the camera refuses to take any pictures. I've even set the shutter speed up to 8 seconds and it still refuses to shoot.
Am I missing something or is it not possible to use the Sigma for night time work?